Some handheld computing devices such as smart phones can provide a variety of different optical functions such as one-dimensional (1D) or three-dimensional (3D) gesture detection, 3D imaging, proximity detection, ambient light sensing, and/or front-facing two-dimensional (2D) camera imaging. Proximity sensor modules can be used, for example, to detect the distance to (i.e., proximity of) an object up to distances on the order of about one meter. Integrating a proximity sensor into a device such as a smart phone or other handheld device, however, can be challenging because space in the host device typically is at premium. Thus, there is a need to achieve accurate proximity sensor modules having a relatively small foot print.